▪ Abstract DNA topoisomerases solve the topological problems associated with DNA replication, transcription, recombination, and chromatin remodeling by introducing temporary single- or double-strand breaks in the DNA. In addition, these enzymes fine-tune the steady-state level of DNA supercoiling both to facilitate protein interactions with the DNA and to prevent excessive supercoiling that is deleterious. In recent years, the crystal structures of a number of topoisomerase fragments, representing nearly all the known classes of enzymes, have been solved. These structures provide remarkable insights into the mechanisms of these enzymes and complement previous conclusions based on biochemical analyses. Surprisingly, despite little or no sequence homology, both type IA and type IIA topoisomerases from prokaryotes and the type IIA enzymes from eukaryotes share structural folds that appear to reflect functional motifs within critical regions of the enzymes. The type IB enzymes are structurally distinct from a...

DNA topoisomerases: structure, function, and mechanism.

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Micro Total Analysis Systems. 1. Introduction, Theory, and Technology

Mitosis and cytokinesis are undoubtedly the most spectacular parts of the cell cycle. Errors in the choreography of these processes can lead to aneuploidy or genetic instability, fostering cell death or disease. Here, I give an overview of the many mitotic kinases that regulate cell division and the fidelity of chromosome transmission.

Mitotic kinases as regulators of cell division and its checkpoints

Defects in cell-death pathways are hallmarks of cancer. Although resistance to apoptosis is closely linked to tumorigenesis, tumour cells can still be induced to die by non-apoptotic mechanisms, such as necrosis, senescence, autophagy and mitotic catastrophe. The molecular pathways that underlie these non-apoptotic responses remain unclear. Several apoptotic and non-apoptotic pathways of cell death have been defined in normal physiology and during tumorigenesis, and these could potentially be manipulated to develop new cancer therapies. The mitotic-checkpoint molecule survivin — the inactivation of which induces the death of p53-deficient cells by mitotic catastrophe — is of particular interest.

http://www.dipbsf.uninsubria.it/labfarmaco/morte%20cellulare/Okada.pdf

Pathways of apoptotic and non-apoptotic death in tumour cells.

Structural biology of Rad50 ATPase: ATP-driven conformational control in DNA double-strand break repair and the ABC-ATPase superfamily.

ATP-Dependent Positive Supercoiling of DNA by 13S Condensin: A Biochemical Implication for Chromosome Condensation

13S condensin is a multisubunit protein complex essential for mitotic chromosome condensation in Xenopus egg extracts. Purified 13S condensin introduces positive supercoils into DNA in the presence of topoisomerase I and adenosine triphosphate in vitro. The supercoiling activity of 13Scondensin was regulated by mitosis-specific phosphorylation. Immunodepletion, in vitro phosphorylation, and peptide-mapping experiments indicated that Cdc2 is likely to be the kinase that phosphorylates and activates 13S condensin. Multiple Cdc2 phosphorylation sites are clustered in the carboxyl-terminal domain of the XCAP-D2 (Xenopus chromosome-associated polypeptide D2) subunit. These results suggest that phosphorylation of 13Scondensin by Cdc2 may trigger mitotic chromosome condensation in vitro.

http://science.sciencemag.org/content/sci/282/5388/487.full.pdf

Phosphorylation and Activation of 13S Condensin by Cdc2 in Vitro

http://pbsb.med.cornell.edu/pdfs/Hayama_3_Cozzareli.pdf

13S Condensin Actively Reconfigures DNA by Introducing Global Positive Writhe: Implications for Chromosome Condensation

https://www.jbc.org/content/276/8/5417.full.pdf

Chromosome condensation by a human condensin complex in Xenopus egg extracts.

Condensin is a multisubunit protein complex that reconfigures DNA structure in an ATP-dependent manner in vitro and plays a central role in mitotic chromosome condensation in Xenopus egg cell-free extracts. The Xenopus 13S condensin complex (13SC) is composed of two subcomplexes: an 8S core subcomplex (8SC) consisting of two structural maintenance of chromosomes (SMC) subunits (XCAP-C and -E) and an 11S regulatory subcomplex (11SR) containing three non-SMC subunits (XCAP-D2, -G, and -H). We report here the biochemical and functional dissection of this chromosome condensation machinery. Although both 8SC and 13SC can bind to DNA in vitro and contain the SMC ATPase subunits, only 13SC is active as a DNA-stimulated ATPase and supports ATP-dependent supercoiling activity. In the cell-free extracts, 13SC is the active form that binds to chromosomes and induces their condensation. Neither 11SR nor 8SC alone is able to bind to chromatin. Our results suggest that the non-SMC subunits have dual roles in the regulation of condensin functions: one is to activate SMC ATPases and the other is to allow the holocomplex to associate with chromatin in a mitosis-specific manner.

https://www.pnas.org/content/pnas/97/22/11972.full.pdf

Keiji Kimura

Papers

ATP-Dependent Positive Supercoiling of DNA by 13S Condensin: A Biochemical Implication for Chromosome Condensation

Phosphorylation and Activation of 13S Condensin by Cdc2 in Vitro

13S Condensin Actively Reconfigures DNA by Introducing Global Positive Writhe: Implications for Chromosome Condensation

Chromosome condensation by a human condensin complex in Xenopus egg extracts.

Dual roles of the 11S regulatory subcomplex in condensin functions